AU718693B2

AU718693B2 - Impact printer with yielding platen

Info

Publication number: AU718693B2
Application number: AU62416/96A
Authority: AU
Inventors: Attilio De Ambrogio; Massimo Oberto; Gianrico Scarton
Original assignee: Olivetti SpA; Ing C Olivetti and C SpA
Current assignee: Shenzhen Pu Ying Innovation Technology Corp Ltd
Priority date: 1995-07-12
Filing date: 1996-06-28
Publication date: 2000-04-20
Anticipated expiration: 2016-06-28
Also published as: EP0800458B1; US5879091A; DE69606518T2; CA2199625A1; DE69606518D1; CA2199625C; ITTO950589A0; IT1276494B1; WO1997002954A1; EP0800458A1; ATE189426T1; AU6241696A; ITTO950589A1; ES2143208T3

Abstract

PCT No. PCT/IT96/00135 Sec. 371 Date Mar. 12, 1997 Sec. 102(e) Date Mar. 12, 1997 PCT Filed Jun. 28, 1996 PCT Pub. No. WO97/02954 PCT Pub. Date Jan. 30, 1997An impact printer (30) comprises a printhead (31) traversing along a guide for printing a line on a document (32) of thickness S, and is provided with contrast means for supporting the document (32) against the head (31) and for contrasting the impact force exerted by the latter against the document. The printhead (31) bears a spacing roller (34) which causes the contrast means to yield in order to compensate for thickness S, which varies according to the document (32), and thus maintain the distance D between the head (31) and the document (32) constant. The contrast means comprise a flexible platen (33) attached yieldingly at the ends, of length at least equal to or greater than that of the print line and having a variable section frame so that the pressure generated between the platen (33) and the roller (34) is substantially constant all along the print line.

Description

IMPACT PRINTER WITH YIELDING PLATEN Field of the Invention The present invention relates to an impact printer and a platen for use therein.

Background Art A known impact printer is represented diagrammatically in Fig. 1, wherein it is labelled 10. A frame 11 of the printer 10 supports two springs 12 that act on the ends 18 of a platen 13, ideally rigid type and on which a .:oo.i S°document 14 rests. A needle printhead 16, or known type, moves in a fixed rectilinear trajectory along the document 14 for printing characters on the document 14 through the interposition of an ink ribbon not shown in the drawings, and bears a spacing roller 17, which presses the document 14 against the platen 13 during movement of the head 16. In this way, the springs 12 become deformed and thus allow the platen 13 to move with respect to the head 16 and adapt itself to thickness S of the document 14, so that the roller 17 keeps the document 14 at a constant distance D from the head 16, regardless of thickness S of the document.

A pressure P that the roller 17 exerts on the document 14 varies considerably during movement of the head 16. In fact the roller 17, when in proximity of one of the two ends 18 of the platen 13, is contrasted solely by a force corresponding to the elastic reaction of one of the springs 12, whereas, as the head 16 approaches the centre of the platen 13, as indicated by the -2dashed line in Fig. 1, this force tends to increase and become theoretically, assuming null flexibility of the platen 13, twice that at the ends of the platen 13 and corresponding to the yielding of both springs 12.

The pattern of P is illustrated in graphic form in Fig. 2 by a curve 19 which, for a given thickness S of the document 14, represents the variation of the pressure generated between the roller 17 and the platen 13, along an entire length L of the platen 13; the value assumed by the pressure P in proximity of the two ends 18 of the platen 13 is indicated with Pest, while the value assumed at the centre L/2 is indicated with Pmax.

Variation of the pressure of the spacing roller on the document during head movement gives rise to numerous drawbacks, notably: the likelihood of the roller 17 making a mark on the document, especially if the latter comprises carbon copy sheets or tracing paper, by passing over it during movement of the head or during feeding of the document when a line oo .t feed is effected; variable printing density along the print line when the printhead is impact type, a needle printer for example. In this case, in fact, the elements of the printhead that touch the document exchange energy with the bar, and printing density may be greater at the centre of the line, where the platen contrasts the head with a pressure twice that exerted on the ends, where printing may appear faint. To the detriment of printing density, in fact, the platen tends to dynamically absorb a greater portion of the energy of the head impact elements at its ends, where it contrasts the head with a pressure markedly lower (approximately half) than at the centre of the bar.

Moreover, if a sufficient printing density is also desired in proximity of the ends of the platen and not solely at the centre, the force exerted by the springs on the ends must be increased, but this requirement conflicts with that of reducing the force in order to avoid the roller causing marks on the document at the centre of the bar.

3 SUMMARY OF THE INVENTON According to a first aspect of the present invention there is provided an impact printer comprising: a printhead arranged so as to travel along a guide for printing a print line of a predetermined length on a document; contrast means for opposing the impulse exerted by said printhead during printing of said line, said contrast means including a flexible platen having two opposite ends and a center, said two ends resting on yielding supports and spaced apart by a distance at least equal to said length of said print line, said flexible platen being manufactured from a material with modulus of elasticity E and having a moment of inertia J with respect to its longitudinal barycentric plane; °ooo° S°spacing means borne by said printhead and arranged so as to cooperate with said contrast means in order to maintain a constant distance between said 15 printhead and said document along said print line; and °resilient pressure means for applying a pressure between said spacing means and said contrast means, said pressure being substantially constant for the entire said length of said print line, characterized in that said flexible platen has a value for the product of said modulus of elasticity E by said moment of inertia J that increases in both directions from the ends towards the center of said platen.

Preferably the flexible platen has a T section.

Alternatively, the flexible platen has a U section.

Advantageously, said contrast means comprises a platen manufactured from a material which yields locally under said pressure.

Alternatively, said platen comprises a profiled strip manufactured from a material which yields under local pressure which is arranged in a top portion of said platen for supporting said document against said printhead.

According to a second aspect of the present invention there is provided a platen for an impact printer, said printer comprising a printhead suitable for impact printing a print line of a predetermined length on a document, wherein Ssaid printhead bears a spacing roller suitable for holding said document at a 3a constant distance from said printhead, said platen having two opposite ends and a center and being suitable for supporting said document against said printhead thereby opposing the impact energy exerted by said printhead on said document during printing said print line, said platen being additionally suitable for exerting a pressure on said spacing roller while said roller moves along said print line, said platen resting at said ends on yielding supports and having an intrinsic flexibility, characterized in that said intrinsic flexibility is summed with the capacity for yield that said yielding supports confer on said platen in order to provide a substantially constant pattern of application of said pressure along said length of said print line.

Typically said platen is manufactured from a material with modulus of elasticity E and a transversal section of said platen has a moment of inertia J S• with respect to its longitudinal barycentric plane, characterized in that the value of the product of said modulus of elasticity E by said moment of inertia J increases in both directions from said ends towards said center of said platen.

According to a third aspect of the present invention there is provided a platen for an impact printer, said platen being of a first length and having two opposite ends which rest on yielding supports having a predetermined capacity for yield, said printer comprising: printing means slidingly movable along a guide for printing by means of an impact energy exerted on a document, a print line of a second length not greater than said first length on said document, said document being supported against said printing means by said platen; spacing means connected by said printing means for holding said document at a constant distance from said printing means by exerting a pressure on said platen while said printing means moves along said print line, characterized in that said platen has an intrinsic flexibility which varies along said first length, said intrinsic flexibility cooperating with said predetermined capacity for yield of said yielding supports, whereby a substantially constant pattern of said pressure is applied along said length of said print line.

3b Preferably, said yielding supports comprise an oscillating arm and a spring, said arm having a first end, a second end opposite to said first end, and a hinging pin intermediate between said first and said second end, said first end being pivotingly attached to said platen by means of a pin, and said spring being set between said platen and said second end.

Advantageously, said platen is manufactured from a material with modulus of elasticity E and a transversal section of said platen has a moment of inertia J with respect to its longitudinal barycentric plane, characterized in that a product of said modulus of elasticity E by said moment of inertia J increases in both directions from the ends towards a center of said platen.

These and other characteristics of the invention will become apparent oo"from the description that follows, provided by way of non-exhaustive example, o°•°o S°taken in conjunction with the accompanying drawings.

°0° BRIEF DESCRIPTION OF THE DRAWINGS S 15 Fig. 1 illustrates a schematic view of an impact printer comprising a 0° platen manufactured according to the prior art; oo. Fig. 2 illustrates the pattern of pressure between the head and the platen in the printer of Fig. 1; °"Fig. 3 illustrates in partial manner a perspective view of the printer and of 20 the platen according to the invention; Fig. 4 illustrates the pattern of pressure between the printhead and the 0 0 oooo platen of Fig. 39 Fig. 5 illustrates a partial longitudinal view of the platen, according to a first embodiment of the invention; Fig. 6 illustrates a transverse section of the platen of Fig. Fig. 7 illustrates a front view, showing details of some of the members of Fig. 3; Fig. 8 illustrates a sectional, view of a second embodiment of the platen according to the invention; and Fig. 9 illustrates a perspective view of a third embodiment of the platen according to the invention.

WO 97/02954 PCT/T96/00135 DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to Fig. 3, a printer 30 is provided with an impact head 31, for example but not necessarily, a needle printhead, and with a platen 33, manufactured from a material having a modulus of elasticity E, on which rests a document 32 to be printed and having a thickness S. The head 31 bears a spacing roller 34 which presses on the document 32 to push it against the platen 33 and maintain it at a fixed distance D from the head 31.

In turn, the platen 33 is set at its ends on yielding supports 36, one only of which is illustrated in Fig. 3, and each comprising a spring 37 and an arm 38 oscillating on a fixed frame 39 of the printer 30. As may be seen plainly in Fig. 7, the spring 37 is set between the arm 38 and the platen 33, whereas the arm 38 has one end attached pivotingly to the platen 33 by means of a pin 43.

In addition, the arm 38 is hinged in an intermediate area between its ends to the frame 39 by means of another pin 44. Thus the arm 38 is suitable for oscillating about frame 39, causing the spring 37 to become deformed, and allowing the platen 33 to move with respect to the head 34, to compensate for thickness S of the documents 32 placed between the platen 33 and the head 31. For limiting travel of the platen 33 whenever not contrasted by roller 34, an abutment element 40 is provided attached to the platen 33, which extends through a hole 45 in the frame 39 and is suitable for abutting against the latter when the head 31 is not disposed above the platen 33 and as a result the roller 34 is not pressing against it.

In addition, the platen 33 is provided with two guide areas 41 and 42 (Fig. arranged along and on opposite sides of the platen itself, with the purpose of guiding passage of the document 32 under the head 31 so that it does not become jammed.

Figs. 5 and 6 illustrate the platen 33 in longitudinal and transverse view respectively, and show that the platen 33, according to a first embodiment of the invention, has a T section, height h of which tends to increase, in the direction from the ends of the platen 33 towards the centre. A generic section VI-VI of the platen 33, like that illustrated in Fig. 6, defines a WO 97/02954 PCT/IT96/00135 horizontal barycentric plane 51 passing through the centre of gravity of this section.

In this embodiment, as is well known to those skilled in the sector art, the moment of inertia J of the section with respect to the plane 51 increases in the direction from the ends of the platen towards the centre, and accordingly also the product of the moment of inertia J by the modulus of elasticity E of the material from which the platen is manufactured increases from the ends towards the centre of the platen. Moreover, as is also known to those skilled in the sector art, the product of the modulus of elasticity E by the moment of inertia J mentioned before is inversely proportional to the capability of the platen 33 to bend under a determined pressure. In other words, the lower the product of E by J, the greater the flexibility of each section of the platen 33 or, to put it the other way round, the higher the product of E by J, the greater the rigidity offered.

The frame of the platen 33, according to this first embodiment, determines a pattern of the product of E by J such that different degrees of flexibility are given to the said platen, which is thus selectively deformable under the pressure exerted on it by the spacing roller 34, and becomes suitable for cooperating with the yielding means 36 so as to contrast the spacing roller 34 with a substantially constant pressure P over its entire length, when the roller 34 moves along the platen. In other words, the platen 33 bends to a different degree under the thrust of the roller 34, while during this bending action the yielding supports 36 yield, and overall behaviour of the platen 33 and of the supports 36 results in a substantially constant pattern of the pressure P all along the entire lenght L of the platen 33.

This substantially constant behaviour of the pressure P, for a given thickness S of the document 32, is illustrated in graphic form in Fig. 4 by the curve 20 which shows how the value of P varies, along the entire lenght L of the platen 33, between Pm. and P. (where and P. are respectively the maximum pressure and the pressure at the ends of the platen 33), such that the following expression holds: P) 2; (1) WO 97/02954 PCT/IT96/00135 If the thickness S increases, the average pressure P also increases, but regardless of the thickness of the document (in practical applications, generally between 0.1 mm and 4 mm), the above expression will always be verified.

The curve 20 is the result of experimental measurements performed by the inventors on a platen constructed as described previously, measurements obtained by moving a dynamometer along the platen and recording at each point the pressure needed to cause a determined constant yielding of that point. Also illustrated in Fig. 4, by means of the curves 21, are some patterns of the pressure P for different values of the thickness S of the document 32.

Verifications were also made of printing quality using a printer in which dimensions were selected for the yielding supports 36 and the flexible platen 33 such that a substantially constant force is generated between the platen 33 and the roller 34 along the entire print stroke of the roller 34, in the vicinity of a value 3 Nw, over a wide range of thicknesses S of documents handled, from about one tenth of a millimetre to 4 mm.

These thicknesses are those of documents, ranging from a single sheet to a banking passbook, whereas the indicative value of 3 Nw defined for the contact force between roller and document was selected both to contrast in optimum fashion the force exerted by the impact members of the head 31 on the platen 33 (a force which on average is always less than 2 Nw), avoiding excessive absorption by the platen of the energy of these impact members and the resultant reduction in printing density, and also to avoid the defect of the roller marking the document.

The platen 33 is preferably manufactured from a plastic material, but may have a mixed type frame, with metallic inserts distributed or located over the entire width of the platen. Also inserted at the top part of the platen 33 is a strip 52 of special plastic, which generally has the function of improving the surface characteristics of the platen 33 in the area that the document 32 rests on.

Fig. 8 illustrates a second embodiment of the platen, in which the platen has an upside-down U section 54, manufactured from a plastic WO 97/02954 PCT/IT96/00135 material, and has a longitudinal profiled part 53, made, for example, of a metal or plastic sheet, arranged inside the U section. The profiled part 53 and the part 54 of plastic material together define the flexibility characteristics of the platen 33, suitable for determining a substantially constant pressure pattern.

Fig. 9 represents a third embodiment of the platen, formed by a body 56 of yielding material, for example rubber. A profiled strip 57, made, for example, of a metal or plastic sheet, is attached on the upper part of the body 56 and defines a support plane 58 for the document 32 and two guide l0 planes 59 and 61 for guiding the document 32 towards the plane 58 and to the outlet from the plane. The strip 57 is additionally provided with a plurality of notches 62 in the planes 59 and 61, suitable for conferring greater flexibility to the strip 57 during deformation of the platen 33.

It will be apparent that changes and/or improvements may be made to the printer of this invention, without exiting from the scope of the invention.

Claims

1. An impact printer comprising: a printhead arranged so as to travel along a guide for printing a print line of a predetermined length on a document; contrast means for opposing the impulse exerted by said printhead during printing of said line, said contrast means including a flexible platen having two opposite ends and a center, said two ends resting on yielding supports and spaced apart by a distance at least equal to said length of said print line, said flexible platen being manufactured from a material with modulus of elasticity E and having a moment of inertia J with respect to its longitudinal barycentric plane; spacing means borne by said printhead and arranged so as to cooperate with said contrast means in order to maintain a constant distance between said printhead and said document along said print line; and 15 resilient pressure means for applying a pressure between said spacing °o°°o means and said contrast means, said pressure being substantially constant for the entire said length of said print line, characterized in that said flexible platen has a value for the product of said modulus of elasticity E by said moment of inertia J that increases in both directions from the ends towards the center of said platen.

2. An impact printer according to claim 1, characterized in that said flexible Splaten has a T section.

3. An impact printer according to claim 1, characterized in that said flexible platen has a U section.

4. An impact printer according to claim 1, characterized in that said contrast means comprises a platen manufactured from a material which yields locally under said pressure. 9 An impact printer according to claim 4, characterized in that said platen comprises a profiled strip manufactured from a material which yields under local pressure which is arranged in a top portion of said platen for supporting said document against said printhead.

6. A platen for an impact printer, said printer comprising a printhead suitable for impact printing a print line of a predetermined length on a document, wherein said printhead bears a spacing roller suitable for holding said document at a constant distance from said printhead, said platen having two opposite ends and a center and being suitable for supporting said document against said printhead thereby opposing the impact energy exerted by said printhead on said document during printing said print line, said platen being additionally suitable for exerting a pressure on said spacing roller while said roller moves along said print line, said platen resting at said ends on 15 yielding supports and having an intrinsic flexibility, characterized in that said oooo intrinsic flexibility is summed with the capacity for yield that said yielding supports confer on said platen in order to provide a substantially constant *o pattern of application of said pressure along said length of said print line.

7. A platen according to claim 6, in which said platen is manufactured from :a material with modulus of elasticity E and a transversal section of said platen :has a moment of inertia J with respect to its longitudinal barycentric plane, characterized in that the value of the product of said modulus of elasticity E by said moment of inertia J increases in both directions from said ends towards 25 said center of said platen.

8. A platen for an impact printer, said platen being of a first length and having two opposite ends which rest on yielding supports having a predetermined capacity for yield, said printer comprising: printing means slidingly movable along a guide for printing by means of an impact energy exerted on a document, a print line of a second length not greater than said first length on said document, said document being supported 10 against said printing means by said platen; spacing means connected by said printing means for holding said document at a constant distance from said printing means by exerting a pressure on said platen while said printing means moves along said print line, characterized in that said platen has an intrinsic flexibility which varies along said first length, said intrinsic flexibility cooperating with said predetermined capacity for yield of said yielding supports, whereby a substantially constant pattern of said pressure is applied along said length of said print line.

9. A platen according to claim 8, characterized in that said yielding supports comprise an oscillating arm and a spring, said arm having a first end, a second end opposite to said first end, and a hinging pin intermediate between said first and said second end, said first end being pivotingly attached to said platen by 15 means of a pin, and said spring being set between said platen and said second end. A platen according to claim 8, in which said platen is manufactured from a material with modulus of elasticity E and a transversal section of said platen has a moment of inertia J with respect to its longitudinal barycentric plane, oo. characterized in that a product of said modulus of elasticity E by said moment of •go inertia J increases in both directions from the ends towards a center of said platen. 25 11. An impact printer substantially as herein before described with reference to the accompanying drawings, other than those which illustrate the prior art.

12. A platen substantially as herein before described with reference to the accompanying drawings, other than those which illustrate the prior art. 11 Dated this 17th day of February 2000 ING. C. OLIVETTI S.p.A. By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia 4 4. **age a*